In the manufacture of a three-dimensional article, it is common practice to first create a design of the article and then produce a prototype of the article. After reviewing the initial design and prototype, design revisions are often made requiring the production of yet another prototype. This process of review and redesign may be repeated a number of times before finding the desired design, thereby requiring that one or more prototypes be produced. Accordingly, the process of designing and prototyping an article may involve a considerable expense of time, effort and money.
Computer aided design (CAD) systems are commonly used for automating the design process. With the aid of a computer, an operator is able to design a three-dimensional article and display the design on a two-dimensional medium, such as a display screen or paper. The computer aids in the design as called for by the operator according to pre-existing design parameters and computer software.
Computer aided milling machines for milling articles in response to computer generated signals are also commonly used to make certain articles. In these machines, a computer generated data file representative of the article to be produced is used to control the operation of the machine. Milling tools within the machine shape a body of material. Relatively coarse tools may be used to shape coarse features, while relatively finer tools may be used to finish the article. These machines, however, are relatively large, expensive and limited in the article geometries that may be produced.
Accordingly, systems have been developed wherein a three-dimensional article is constructed in successive layers based upon three-dimensional CAD data. For example, stereolithography is one approach to producing a prototype of an article layer by layer. An example of the production of prototypes through stereolithography is disclosed in U.S. Pat. No. 4,575,330 to Hull entitled "Apparatus for Production of Three-Dimensional Objects By Stereolithography." Hull discloses an apparatus whereby articles are produced by forming successive, adjacent, cross-sectional laminae of the article at the surface of a fluid medium. The fluid medium is capable of altering its physical state from a fluid to a solid in response to stimulation, such as by UV radiation; particle bombardment such as electron beams; chemical reaction; or impinging radiation other than UV radiation. The apparatus includes a source of stimulation which may be selectively applied to the surface of the fluid medium to produce the cross-sectional laminae of the article. The source of selective stimulation is controlled by a computer in response to coordinate data.
Stereolithography, however, requires the use of more material than is actually incorporated in the article being produced, and also requires the exact placement of the article being constructed relative to the surface of the fluid medium. In addition, the depth of the layer created when the fluid surface is exposed to the stimulation may be difficult to control.
An apparatus and method for forming three-dimensional articles from a material which is normally solid but flowable when heated is disclosed in U.S. Pat. No. 5,141,680 to Almquist et al. entitled "Thermal Stereolithography." This patent discloses an apparatus including a nozzle for dispensing a material which has been heated to the point that it flows. The resolution of the final part is determined by the size of the outlet in the dispensing nozzle. The material is dispensed through the nozzle by applying pressure, and the flow of material can be stopped by means of a slidable valve or by lessening, ceasing, or reversing the pressure. Accordingly, precise control of the flow of material may be difficult and high accuracy of the article may be difficult to obtain.
U.S. Pat. No. 5,121,329 to Crump entitled "Apparatus and Method for Creating Three-Dimensional Objects" discloses another apparatus wherein a flow of material through a nozzle is used to create a three-dimensional object. The flow of material is determined by the size of the outlet orifice, a constant pressure, and the vertical height of the tip of the nozzle. In addition, a spring-loaded ball check valve may assist in metering the flow of material. Again, precise control of material flow may be difficult to obtain.
A major advance in the art of three-dimensional modeling is disclosed in U.S. Pat. No. 4,665,492 to Masters entitled "Computer Automated Manufacturing Process and System." This patent discloses an apparatus including: an ejection head having an ejection nozzle for emitting small mass particles of particulate matter; a servo-mechanism for manipulating the ejection head and nozzle; and a machine controller for controlling the servo-mechanism in response to a data file containing coordinate information representing the design of the article being produced. The mass particles are directed to the coordinates of a three-dimensional article as defined by the computer data file. The mass particles may include plastic material, a slurry material having water content, and charged particles which are electrically deflected.
A method and apparatus for forming three-dimensional solid form objects is disclosed in U.S. Pat. No. 5,257,657 to Gore entitled "Method for Producing A Solid-Phase Object From A Material in the Liquid Phase." According to this patent, droplets of a liquid-phase material are ejected to form a spheroid. The size of the droplet is usually preset and the ejection frequency is usually varied to change the mass of material delivered. This method, however, may not work well for glasses and plastics which do not have a set transition temperature at which they become rigid.
Another method and apparatus for forming three-dimensional objects is disclosed in U.S. Pat. No. 5,136,515 to Helinski entitled "Method and Means for Constructing Three-Dimensional Articles by Particle Deposition." This patent discloses a device including two jetting heads, or alternately a single jetting head with two feeder lines. In either embodiment, the controller causes fabrication particle material to be ejected as droplets forming the three-dimensional object, while a complementary support structure is created by the ejection of support particles. While this scheme allows the fabrication of layers having various angles of contact, the three-dimensional object must later be separated from the support structure.
U.S. Pat. No. 5,260,009 to Penn entitled "System, Method, and Process for Making Three-Dimensional Objects" discloses another apparatus for forming three-dimensional objects wherein a second material is dispensed with each layer of the three-dimensional article as it is formed. In this patent, the ejector aperture is varied to change the dispensing volume and the resulting resolution.
The formation of three-dimensional articles by jetting a photosetting or thermosetting material is disclosed in U.S. Pat. No. 5,059,266 to Yamane et al. entitled "Apparatus and Method for Forming Three-Dimensional Article." A jet sequentially or intermittently jets the photosetting or thermosetting material in a droplet form along a flight passage to the stage. An exposure unit is then used to cure the material. In this patent, the amount of resin is varied by providing a first jet having a large jetting amount for greater building speed, and a second jet having a smaller jetting amount for greater resolution or definition. Unfortunately, this approach is more complicated as it requires two different jets, and two associated material delivery systems. Furthermore, the higher building speed still results in lower definition or resolution.
There is an interrelationship between: the carriage speed of a dispensing head, that is, the speed at which the head may be moved; the amount of material that is delivered; the resolution of the features of the article; and the build rate that may be achieved. In other terms, smaller amounts of material may be delivered accurately resulting in an article having a finer resolution. This advantage, however, is traded off against the relatively high carriage speed that may be required to construct the article at a sufficient overall speed.
Other U.S. patents related to three-dimensional modeling are listed as follows: U.S. Pat. No. 5,207,371 to Prinz et al.; U.S. Pat. No. 5,301,415 to Prinz et al.; U.S. Pat. No. 5,301,863 to Prinz et al.; U.S. Pat. No. 5,140,937 to Yamane et al.; U.S. Pat. No. 5,149,548 to Yamane et al.; U.S. Pat. No. 5,204,124 to Secretan et al.; U.S. Pat. No. 4,749,347 to Valavaara; U.S. Pat. No. 5,303,141 to Batchelder et al.; U.S. Pat. No. 5,031,120 to Pomerantz et al.; and U.S. Pat. No. 5,287,435 to Cohen et al.
Accordingly, there is a need in the art for a relatively simple, reliable, and inexpensive method and apparatus for quickly producing accurate three-dimensional articles having complex shapes and features based on article defining data wherein the build rate and resolution can be easily and controllably varied as an article is being produced.